A transmission system for a vehicle is suitably configured to deliver improved power transmitting efficiency, and improved fuel efficiency. A conventional transmission mechanism may be a manual transmission, a conventional stepped automatic transmission, a continuously variable transmission, a double clutch transmission, or other type of vehicle transmission. Such transmissions are typically used with conventional gasoline or diesel engine systems.
By contrast, electric vehicles are equipped with electric motors, and hybrid electric vehicles may have electric motor(s) in combination with a combustion engine. In such vehicles, a transmission containing a transmission fluid is provided that is separate from an electric motor and electric motor oil used to power the transmission.
In a hybrid electric transmission, the transmission fluid may be in contact with parts of the electric motor or a similar fluid may be used for both the transmission and for cooling and lubricating the motor. For example, the lubricating and cooling fluid for the motor may be in contact with electrical windings in the stator, in order to efficiently cool the electric motor and to insulate the electrical parts to prevent a short circuit of the electric motor. Accordingly, such fluid desirably has a relatively low electrical conductivity so that the electric motor can operate properly without short-circuiting.
A hybrid vehicle 10 is illustrated schematically in FIG. 1 and may contain an engine 12 and transmission 14 for powering wheels 16 of the vehicle 10. The transmission 14 may include an electric motor 18 and a power transfer/gear reduction unit 20 coupled to the wheels 16. A common lubricant reservoir 22 may contain a lubricant composition as described herein for lubricating both the electric motor 18 and the power transfer/gear reduction unit 20.
A lubricant additive that contributes to an increase in electrical conductivity is a metal containing detergent. Such detergents are required to be present in an amount that enables the fluid to provide suitable anti-rust performance. Accordingly, there is a tension between providing lower amounts of detergent in order to achieve suitable electrical conductivity for the fluid and higher amounts of detergent required to provide suitable anti-rust performance.
With the current trend toward more energy efficient vehicles, it is desirable to provide a multipurpose or dual-purpose lubricating fluid that may be used to lubricate mechanical components as well as provide lubrication and cooling to electromechanical components in electric vehicles and/or hybrid electric vehicles. Accordingly, it is desirable to provide a fluid that may meet electric motor oil requirements, such as lower electrical conductivity, cooling capability (high heat capacity, high thermal conductivity), and low Noack volatility, in addition to lubricity requirements for a transmission, such as a manual transmission, an automatic transmission, a continuously variable transmission, or a double clutch transmission.
In view of the foregoing, embodiments of the disclosure provide a dispersant additive composition, a lubricant composition containing the dispersant additive, a transmission containing the dispersant additive, and a method of providing a versatile lubricating fluid. The dispersant includes a reaction product of a hydrocarbyl substituted carboxylic acid or anhydride and an amine. The reaction product has a nitrogen content up to 10,000 ppm by weight, and a boron plus phosphorus to nitrogen ((B+P)/N) weight ratio of from 0:1 to about 0.8:1. The dispersant additive composition in combination with a metal detergent is effective to provide an electrical conductivity to a lubricant composition of less than about 1700 pS/m.
Another embodiment of the disclosure provides a transmission that includes an electric motor and a lubricating fluid. The lubricating fluid is in contact with said electric motor; and includes (1) an oil of lubricating viscosity; and (2) a dispersant additive composition including a reaction product of a hydrocarbyl substituted carboxylic acid or anhydride and an amine. The reaction product has a nitrogen content up to 10,000 ppm by weight and a boron plus phosphorus to nitrogen ((B+P)/N) weight ratio of from 0:1 to about 0.8:1. The dispersant additive composition in combination with a metal detergent is effective to provide an electrical conductivity to a lubricant composition of less than about 1700 pS/m.
Other embodiments of the disclosure provide a lubricating composition for a hybrid vehicle. The lubricating composition includes (1) a base oil of lubricating viscosity; (2) a dispersant additive derived from a hydrocarbyl substituted carboxylic acid or anhydride and an amine; and (3) a metal-containing detergent. The dispersant additive has a content up to 10000 ppm by weight, and a boron plus phosphorus to nitrogen ((B+P)/N) weight ratio of from 0:1 to about 0.8:1. The dispersant additive plus metal-containing detergent is effective to provide the lubricating composition with an electrical conductivity of less than about 1700 pS/m.
A further embodiment of the disclosure provides a method for providing a versatile lubricating fluid for lubricating a hybrid vehicle. The method includes blending an oil of lubricating viscosity with a dispersant additive and a metal-containing detergent to provide a lubricant composition having an electrical conductivity of less than about 1700 pS/m. The dispersant additive has a nitrogen content up to 10,000 ppm by weight and a boron plus phosphorus to nitrogen ((B+P)/N) weight ratio of from 0:1 to about 0.8:1.
In one embodiment, the dispersant is a succinimide dispersant.
In another embodiment, the metal-containing detergent is present in an amount that is sufficient to provide from about 60 to less than about 600 ppm by weight metal to the lubricant composition.
Additional features and advantages of the disclosure may be set forth in part in the description which follows, and/or may be learned by practice of the disclosure. The features and advantages of the disclosure may be further realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure, as claimed.